Microphone



Patented Nov. 14, 1922.

iran sra'res DAVID G. MGCAA, QF LANCASTER, PENNSYLVANIA.

MICROPHONE.

Application 'filed June 4, 1918. Serial No. 238,177.

T 0 all whom it may concern:

Be it known that I, DAVID G. MoCAA, a citizen of the United States,residing in Lancaster, Pennsylvania, have invented Microphones, of whichthe following is a specication.

One object of this invention is to provide a microphone particularlyadapted for use in wirelesstelephone systems' by reason of its beingcapableof dissipa'ting the relatively large amounts of electrical energycharacteristic of the more successful forms of this class of apparatus,the construction including a novel arrangement of heat radiatingY vanesdesigned to be cooled either by air or'liquid.

A further object of the invention is to provide a microphone whoseconstruction shall be such as to it'it for carrying relatively heavycurrents of electricity, i. e., instead of being limited to use incircuits carrying in the neighborhood of one-quarter of. an ampere, themicrophone constructed according to my invention shall be capable ofcarrying from three to five'ampe'res.

I'also desire to provide a microphone particularly adapted to employ aheat conducting electrical insulator so disposed as to facilitate theradiation of the heat generated in the instrument under conditions ofuse.

Another object of my invention is to provide a device of the class notedwhich shall be particularly adapted for use in a position in which thecarbon granules rest upon and are supported directly by the diaphragm,the construction being such that the instrument is not only efficientbut is sensitive in that for given movements of the diaphragm it givesincreased resistance changes in the circuit in which it is included.

It is also desired that the microphone constituting my invention shallhave its parts so arranged that the heat produced under conditions ofuse shall be generated not between the diaphragm and the granules butbetween the latter and an'interior 'terminal in the form of a carbonbutton.

These objects and other advantageous ends I secure as hereinafter Vsetforth, reference being had tothe accompanying drawings, in which- Fig. lis a central vertical section illustrating the detail construction of amicrophone constructed according to my invention.

Fig. 2is a horizontal section ont-he line 2.-2fFg- 1;

Figs. :f5 @1.1114 are perepetre et the,

conducting plate and damping spring forming part of the instrument shownin Figs. l and 2;

Fig. 5 is a central vertical section of a modified form of microphone;

Fig. 6 is a horizontal section on the line 6 6, Fig. 5; and

Fig. 7 is a perspective view of the form of damping spring preferablyused in that form of instrument shown in Fig. 5.

In Figs. l to 4 of the above drawings, l represents a cup-shaped,substantially cylindrical casing preferably of brass or copper, closedat one end and having threaded to it an inwardly flanged ring 2 designedto clamp over its otherwise open end a carbon diaphragm 3.

The flange of this ring also clamps against the outer portions of saiddiaphragm at two opposite portions thereof, a plate 4 of copper foil(Fig. 3) preferably made with a central circular portion normallypressed against the central part of the diaphragm 3 by the dampingspring 5.

This latter consists of a spring metal strip having mounted on one end acushion 6 of asbestos or other poor heat-conductor and has its oppositeend clamped against the outer edge ofthe ring 2 by a cover plate 7 heldto said ring by screws 8. This plate has an outwardly iianged openingformed through its central part for the reception of a horn ormouthpiece 9 whose open outer end extends in a line at right angles to thatof the center line of the casing l' and of the cover plate 7.

Mounted centrally within the casing l is a substantially cylindricalmetal shell l0 extending from the top or upper end thereof to within ashort distance of the diaphragm and a series of radially disposed vanes2l extend between this shell and the curved portion of the casing l insuch numbers as to rapidly conduct heat to the latter from said shell,it being obviously immaterial whether or not the vanes, shell and casingare integral or are structurally independent but in intimate contact.

Mounted within the shell 10 is an inverted cup-shaped container 11 whichaccording to my invention is characterized by being not only a poorelectrical conductor but a good conductor of heat and as typical of amaterial answering this requirement, I preferably employ soapstoneor'talc.

Said container 11 is centrally .recessed De provide a chamber into whichextends a conk ductor 12 in the form of a threaded rod which within therecess 13 has mounted upon it terminal member formed by a carbon but ton14 between which and the top of said cavity are confined one or moremetal wash` ers 15. The conductor 12 is insulated from the casing 1 andhas mounted on its outer end a metal washer 16 and a retaining nut 17whereby it with the button 14 are rigidly held in place. y, l

Within the cavity 13 surrounding and engaging the carbon terminal memberle, is a mass of carbon granules 13 which when the casing 1 is in itsnormal operative position shown, rest upon and are supported by thediaphragm 3, it being noted that while the insulating cup 11 is spacedaway trom said diaphragm so as not to interfere with its tree vibration,the distance between these niembers is not sutlicient to permit escapeoiE the granules 18.

In order to prevent air packing, l provide a set of openings 19 into thecells o r compartments formed bythe vanes 21. shell 10 and casing 1 andother openings 2O in the flat top ot said casing so that there is a freeflow of cooling Huid such as air into and out ot said chambers orcavities.

Under conditions of use the instrument is supported by any suitablemeans in the position shown in Fig. 1, that is, with its carbon granules18 resting upon and supported by the diaphragm 3 as well as engaging thecarbon button 14. As a result of this construction and position, thediaphragm is vibrated and when current iiows through the centralconductor l2, the carbon button 14, the granules 18. the diaphragm 3 anda second terminal (not shown) electrically connected to the casing 1,there is practically no heat generated between said granules and thediaphragm.

(Jn the other band by tar the greater quantity of the energy dissipatedoccurs in the form ot heat produced between the carbon granulesV and thecarbon button or terminal member 14 and because oi the heat conductingcharacteristic of the granule container or cup 11, this heat is rapidlytransferred to the shell 10 and thence through the vanes 21 to the outeror main casing 1, being quickly dissipated by the air both inside andoutside of this latter. As a result, relatively large currents may besafely and continuously employed in the instrument. A The asbestos orother non-conducting cushion 6 on the damping spring 5 electul allyprevents this latter being affected by any heating of the diaphragmwhich may Occur and'such heating is in any event materially reduced bythe use of the body 4 'of metal foil which rapidly conducts the heatfrom the center of said diaphragm to) the parts 1 and 2 ot the casing,from which the dissipation ot heat is aided by the cir culation of airthrough the openings 19 and 20. a i

In that form ot my invention shown in Fig. 5 I have substituted a metalring for themain part ot' the casing land before hold the diaphragm 3and the body' of metal toil 4 to the lower end or edge 'of this ring bya clamping ring 2, likewise damping the vibration of the diaphragm andmaintaining the foil body 1l in intimate engagement with the center otthe latter by a cushion 6L on the end of a damping spring 5a which asbefore is clamped to the ring 2 by a cover plate 7.

The main casing in this case takes the form of a substantiallycylindrical shell 23 having an upward tubular extension 24 in which, asbefore, 1 mount an electrical insulating heat conducting cup orcontainer 25 having a portion projecting into the extension 24. 4Asbefore, a conductor in the form oi a rod 26 threaded at its ends extendsthrough the extension into the cup 25 in which it has mounted on it acarbon button or terminal member 14:a engaging a metal washer 152l whichit holds against the top of the cavity in said cup. The conductor 26with its attached parts, is held in place 4by a nut 17 threaded on itsouter end and engaging a metal washer '16.

In this instance the casing 23-24: is integral with the ring 22, towhich it is connected by a'radially extending portion 28. The carbongranules 18 are as before supported by the diaphragm 3 within the cavity13 of the insulating structure 25 and extend around and in contact withthe carbon button 14a. In order to rapidly dissipate the heat generatedunder operating conditions between said button and said granules. lattach to or :torm integra-l with the shell 23 and its extension 24aseries of radiating vanes 21a whose sides are in tree contact with theair.

As before, there is a? horn or mouth piece 9 extending at right anglesfrom the central opening 30 of the cover plate T and therefore at rightangles to the center line ot the instrument, which as in the case shownin Fig. 1, is designed for use in the position shown in Fig. 5 with thecarbon granules carried upon and in intimate contact with the diaphragm3. This'torm of the inven tion,`like that of Figs. 1 and 2, is alsocapable of operation with relatively heavy currents and is adapted todissipate without injury the relatively large amounts of heat generated.

` I claim Y l Y 1. The combination ina microphone of an invertedcup-shaped container formed of a heat conducting insulator; a metallicshell surrounding, the container; a diaphragm normally closing theotherwise open end of said container; a terminal member extending intothe container; a body ot granular electrical conducting material restingon and supported in the container by; the diaphragm; and heat radiatingelements formed integral with the shell of said container fordissipating heat generated between granular material and: the terminalmember f 2. The combination in a microphone of a soap stone container; aterminal member eX- tending into the same; a diaphragm torming a closurefor said container; and a body of granular electrical conductingmaterial retained in the container by the diaphragm and electricallyconnecting the latter with the terminal member.

3. The combination in a microphone oi' a soap stone container;'aterminal member extending into the same; a diaphragm forming a closurefor said container; a body of granular conducting material retained inthe container by the diaphragm and elect ically connecting the latterwith the terminal member; a metal shell surrounding the container; andheat radiating vanes conductively associated with said shell.

4. The combination in a microphone of a metal casing; a metal shellmounted Within the same; heat radiating vanes connecting said casing andshell; a body of heat conducting electrically insulating material Withinthe shell and formed With a bottomopening cavity; a diaphragm closingsaid cavity; a terminal member'extending into the cavity; and a mass ofgranular conducting material retained by the diaphragm in said cavity inposition to electrically connect it with the terminal member.

The combination in a microphone ot' a casing; a container made of goodheat conducting electrically insulating material and mounted Within thecasing; a diaphragm normali)7 closing the container; a terminal memberextending into the container; and a mass of granular electricalconducting material connecting said terminal member with the diaphragm,there being `openings into the space between the container and thecasing for the admission and exit of cooling iuid.

6. The combination in a microphone of a cellular metal casing havingopenings into its compartments; a container of heat conducting;electrical insulating material within the casing; a terminal memberWithin the container; a diaphragm forming a closure for the container,and a body of granular electrically conducting material connecting thediaphragm With the terminal member.

7. The combination in a microphone of a diaphragm; a terminal member; abody of granular electrical conducting material confined between thediaphragm and said member in position to be supported by said diaphragm;with a damping member in the form of a spring rigidly held at one endand having a heat insulating cushion on its opposite end positioned toexert preseure upon the diaphragm.

8. The combination in a microphone ot a carbon diaphragm; a containernormally closed by said diaphragm; a terminal member in the container; abody of granular electrical conducting material in the con'- tainerelectrically connecting the diaphragm and the conducting member; a bodyot metal foil extending across the diaphragm; vith a damping springincluding a heat insulating cushion engaging the metal foil in positionto act through the same upon the central part of the diaphragm.

9. rlhe combination in a microphone ot a soap stone container having abottom opening; an electrical conductor extending into the container; acarbon button on said con ductor Within the casing; a carbon diaphragmnormally closing the opening of the container; with a body of granularcarbon supported by the diaphragm and in electrical engagement With thecarbon button.

l0. The combination in a microphone of a soap stone container havingabottom opening; an electrical conductor extending into the container; acarbon button on said conductor Withn the casing: carbon diaphragmnormally closing the opening oitz the container; a body of granularcarbon supported by the diaphragm and in electrical eigagement With thecarbon button; and means tor radiating the heat generated between thegranular carbon and the carbon button, consisting of heat radiatingmetal vanes in intimate mechanical connection with the external surfaceof the soap stone container.

In Witness Whereoil I aiiiX my signature.

DAVID Gf lllcAA..

